Supersaturation, induction period, and metastable zone width of CaCl 2 -Na 2 CO 3 -HCl system

The supersaturation, induction period, and metastable zone width of an aqueous supersaturated solution of CaCl 2 -Na 2 CO 3 -HCl system are studied in the present paper. The supersaturation is varied and predicted within a reasonable accuracy when a specified amount of HCl (aq) is added into the aqueous supersaturated CaCl 2 -Na 2 CO 3 solution. It is found that the decrease of solution supersaturation at low pH is caused mainly by the decrease of carbonate ions. Then, the induction periods are estimated by using the coagulation theory and they can be expressed as a function of supersaturation alone, which results from different values of reagent concentration and pH. Finally, the theoretical metastable zone widths based on arbitrary induction periods are obtained. Meanwhile, the induction periods are measured at various levels of reagent concentration and solution pH by applying the conductivity method. Accordingly, the metastable zone widths are determined experimentally and compared with the theoretical results. It is concluded that the present method is an useful tool for determining the metastable zone width of aqueous supersaturated CaCl 2 -Na 2 CO 3 -HCl solution.